שטשאַוו
דער
שטשאַוויי, טשאַוויע, שטשאַוועל

ETYMOLOGY

Beider suggests that the word was borrowed from Old Polish, before the 16th c., when the vowel of szczaw was still long /aː/. The vowel merged with A₂ and had the corresponding different realizations in Yiddish dialects (e.g., "shchūv" in CY).
{Beider 2015: 447}
Herzog writes that in CY שטשאַוו was rendered ščuf, probably because the word entered Yiddish from a Polish dialect where the vowel was /o/, which was then subject to the regular shift o > u in SY. {How widespread was this form?}

CENTRAL

šʲčʲávbɔršt שטשאַוובאָרשט {POLAND, Wolbrom, 50196}

ščav borɩšt שטשאַוו באָרשט {POLAND, Warsaw, 52211}

NORTHEASTERN

Lithuania

s̀c̀ávʲje {LITHUANIA, Vilnius, 54257}